A polarizing film to be used in an image display apparatus (e.g., a liquid crystal display) needs to achieve a high transmittance and a high polarization degree in order to provide bright images with excellent color reproducibility. Conventionally, such a polarizing film is manufactured by aligning a dichroic substance such as iodine that is dichroic or a dichroic dye in a polyvinyl alcohol (PVA)-based polymer film.
In recent years, with an increase in size and improvement in function and brightness of liquid crystal displays, it has been required that polarizing plates to be used therein also are increased in size and improved in optical characteristics (such as neutrality and a polarization degree) and in-plane uniformity. However, in order to obtain a large polarizing plate, it is necessary to perform uniform uniaxial stretching with respect to a wide raw film. However, as the width of the raw film increases, it becomes more difficult to stretch the film uniformly. In fact, uniform stretching is a very difficult treatment, so that, when a wide raw film is used, the resultant polarizing film tends to exhibit degraded in-plane uniformity and optical characteristics. If the in-plane optical characteristics are not uniform, there arises a problem in that display irregularity will occur when the polarizing plate is used to form an image display apparatus. In order to solve this problem, reducing the distance between rolls used for stretching in dry stretching methods has been proposed (see Patent Document 1, for example). However, this cannot solve the problem sufficiently.    Patent Document 1: JP 2002-326278 A